This invention relates generally to a method and apparatus for measuring particle velocity in a solid-gas flow.
Pneumatic transport of coal particles is typically used in coal conversion and combustion processes. Measurement of particle velocity in such a transporting line has significant impact on the safe and efficient operation of a coal plant. Unfortunately, on-line continuous particle-velocity monitoring is still a difficult task. Available techniques have limited industrial application. Commonly employed techniques include the radioactive tracer method, optical techniques, electromagnetic methods, and conventional mechanical approaches. Most of these techniques are either unacceptable or impractical to the coal industry, which normally transports coal at high solid loading rates or recycles char particles under high temperature and pressure. The ideal technique must therefore be able to survive the hostile environment, and be nonintrusive and responsive to a wide range of solid loading rates.
Ultrasonic flowmeters can be designed under several principles and methods. One method is to use the cross-correlation technique, which measures the time-of-flight of a certain inherent flow tag passing through two sensors separated by a known distance. The technique has been demonstrated successfully in monitoring single-phase fluid flows in which turbulent eddies modulate the interrogating ultrasonic beams. This type of correlation flowmeter also has been developed for solid-liquid and gas-liquid mixed-phase flows, in which the density fluctation, caused by solid clusters and gas bubbles, is the prime inherent flow tag.
For solid-gas flows, flowmetering by acoustic methods is extremely difficult because of high acoustic attenuation in gases, high particle impingement noise, and problems associated with impedance mismatch. To date, only qualitative particle velocity indication can be made from the measurement of RMS voltages of the acoustic noise generated in the pipe. Even for this technique, the application is limited to low solid loadings because the sensitivity and linear relationship between noise level and particle velocity diminish with increasing solid loading. Cross-correlation techniques have not been suggested for solid-gas flows because of the difficulty in transmitting an acoustic beam through the medium.
Therefore, it is an object of the present invention to provide a method and apparatus for measuring particle velocity in a solid-gas flow under a wide range of particle concentrations.
It is another object of the present invention to adapt the cross-correlation technique to measure particle velocity in a solid-gas flow.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.